Abstract: Particulate titanium metal matrix composites (MMCs) offer advantages for a wide range of structural applications with increases in stiffness and possibly wear resistance. A powder metallurgy/mechanical alloy route was used successfully to give a fine, uniform distribution of boron in titanium alloy powder. This powder was hot isostatically pressed and during the process TiB reinforcement was formed by an in-situ reaction. Significant tensile ductility in MA titanium alloy (without boron), equivalent to wrought material was achieved, along with good tensile strength. In materials with high TiB volume fractions it is thought that the fine boride size and high strength matrix caused embrittlement. This suggests that the use of a lower strength matrix, such as commercial purity titanium, and shorter milling times would provide a better balance of strength, stiffness and ductility for this type of composite.

Abstract: Boriding of nickel (Ni) has been performed by means of a powder-pack method using boriding powder that contains no silicon. In this study, the boride layer was analyzed with an X-ray diffractometer and electron probe microanalyzer (EPMA). We studied the high-temperature hardness and the friction and wear characteristics of the layer. The results showed that the boride layer was composed of Ni 2 B and that the high-temperature hardness of borided Ni was higher than that of untreated Ni. The friction and wear properties of Ni were improved by boriding.

Abstract: The structure of a nickel-base, self-fluxing alloy coating, containing chromium and boron thermal sprayed and fused, was investigated by x-ray diffraction (XRD), scanning electron microscopy (SEM), electron probe microanalysis (EPMA), and transmission electron microscopy (TEM). A lumpy M6C carbide, a rodlike M3B2 boride of tetragonal structure, a rodlike M7C3 carbide of hexagonal structure, and a Ni-Ni3B eutectic phase formed in the coating after fusing. Metals of M6C, M3B2, and M7C3 phases are composed of chromium, molybdenum, and nickel; chromium and molybdenum; and mainly chromium, respectively. The nickel phase in the coating has the L12 type superlattice structure.

Abstract: A series of experiments were performed to evaluate some properties of borided 99.5% purity nickel. Boronizing was carried out in a solid media consisting of Ekabor powders at 950°C for 2, 4, and 8 h, respectively. Data on intermetallic silicides and borides (Ni 5 Si 2 , Ni 2 B) that formed on the surface of nickel substrate during boronizing were confirmed by a classical metallographic technique and X-ray diffraction (XRD) analysis. It was observed that the predominant phase in the coating layer was a silicide. It is probable that the formation of the nickel silicide layer was due to silicon in the boronizing powder. The hardness of silicides was measured by using a Vickers indenter with a load of 0.5 N. The microhardness of silicides formed on the surface of the nickel substrate reached up to 805 HV. Metallographic studies revealed that the silicide layer has an equiaxed granular morphology, whereas the boride layer formed had a needle-shaped structure. Depending on process temperature and boronizing time the thickness of coating layers ranged from 123 to 281 μm. The thickness of silicide and boride layers depended strongly on the processing time at 950°C. The longer boronizing time resulted in the thicker surface layer. The distribution of alloying elements from the surface to the interior was determined using energy dispersive X-ray spectroscopy (EDS).

Abstract: The stainless steel product has passive film on the surface, and at least one of a conductive metallic inclusion of carbide and a conductive metallic inclusion of boride protrudes through an outer surface of passive film from stainless steel under the passive film. The stainless steel product has low contact electrical resistance and suitable for use in bipolar plates of a polymer electrode fuel cell.

Abstract: Multi-metallic films are prepared from multi-metallic mixtures of metalloamide compounds. The mixtures are subjected to vaporization to form a multi-metallic vapor having defined and controllable stoichiometry. The multi-metallic vapor is then transferred to a chemical vapor deposition chamber, with or without the presence of a reactant gas, to form the multi-metallic film. Multi-metallic nitride, oxide, sulfide, boride, silicide, germanide, phosphide, arsenide, selenide, telluride, etc. films may be prepared by appropriate choice of metalloamide compounds and reactant gas(es).

Abstract: Nanoindentation proves to be an effective technique to measure mechanical properties of “composite” materials, as it has high spatial resolution that enables estimation of properties even from fine grains, particles, and precipitates. The elastic modulus, E, of the composite boride coating deposited on AISI 1010 steel using the laser surface engineering (LSE) process has been computed using the nanoindentation technique. The highest E value of 477.3 GPa was achieved for coating in a sample that contained 0.69 volume fraction of TiB2 particles in the coating after processing with the highest laser traverse speed of 33 mm/s. A comparison between the theoretical and experimental computation of the elastic modulus suggests that theoretical elastic modulus values are lower than computed elastic modulus, as the latter includes the effect of dissolution of fine TiB2 particles in Fe matrix and metastable phase formation such as FeaBb and TimBn. Dissolution of fine TiB2 particles in the Fe matrix in the coating region has been corroborated by transmission electron microscope (TEM) micrographs and corresponding energy-dispersive spectroscope (EDS) analysis and selected area diffraction (SAD) pattern.

Abstract: Gas boronizing was performed at low pressure (100–10 000 Pa) with and without plasma assistance using organoboranes as precursors and hydrogen and argon as carrier gases. The influence of total pressure, boronizing time and both precursor flow rate and hydrogen flow rate on the formation of the boride layer on three steels, 42 CrMo 4 (AISI 4140), C 45 (AISI C1043) and a low carbon steel was investigated. The boride layers were characterized using glow discharge optical emission spectroscopy, X-ray diffractometry, optical microscopy and the pin-on-disc test. With an appropriate choice of process parameters single-phased iron boride layers up to 10 μm of type Fe2B were generated on steel 42 CrMo 4 (AISI 4140) using a borane triethylamine complex as a precursor for gas boronizing and trimethylborate for plasma-assisted boronizing. Carbon was determined to be barely incorporated into the boride layers. First wear tests resulted in a significant wear reduction of plasma-boronized samples compared to untreated samples.

Abstract: The effects of long duration exposure of laser surface engineered composite boride coating on plain carbon steel in air at high temperatures were investigated in this study. Exposures at 600 °C, 800 °C, and 1000 °C for 10, 30, and 50 hours of composite-TiB2 coated samples were conducted to study oxide scale growth and morphology. Kinetics of oxidation of the coating during elevated temperature exposures were separately studied using the thermogravimetric analysis (TGA) technique. The oxidation rate for all samples was parabolic in nature and the oxidation kinetic rate constant, K, increased with increasing temperature of exposure. Activation energy, Q for composite TiB2 coating was found to be 205 kJ/mol. A thick (>35 µm) oxide layer formed for all duration of exposure at temperatures ≥800 °C. In case of 1000 °C exposure, a very thick (>150 µm) oxide layer was formed, which was separated from the substrate. X-ray diffractometry analysis revealed the complex nonstoichiometric nature of the oxides of type TiaOb, FemOn, and FexTiyOz. Profilometric measurements indicated an increase in the surface roughness of the oxide layer with an increase in temperature of exposure. These physical observations indicated that the nature and morphology of the oxides formed at various temperatures and duration of exposure are complex.

Abstract: PROBLEM TO BE SOLVED: To provide a method for producing stainless steel for conductive pars excellent in corrosion resistance and small in the increase of contact electric resistance even in the case of being used for a long time. SOLUTION: In this method for producing stainless steel, stainless steel is corroded in an acidic aqueous solution to expose one or more kinds among M23C6 type, M4C type, M2C type and MC type carbide metallic inclusions and M2B type boride metallic inclusions having electric conductivity to the surface, next, neutralizing treatment is performed in an alkaline aqueous solution of pH 7 or more, and, after that, water washing and drying are furthermore performed. COPYRIGHT: (C)2001,JPO

Abstract: The effect of different boron concentrations on the sintering behavior of an Fe-1.5 pct Mo (wt pct) prealloyed powder was investigated. Sintering was carried out in a dilatometer so that all dimensional changes involved with the densification process could be followed. Several transformations were found to occur by heating powder compacts to 1200 °C and then cooling them to room temperature. At high temperatures, boron promoted the formation of liquid phases that, through a more-efficient sintering kinetics, promoted a satisfactory densification. Faster heating rates also had beneficial effects on the density of the final products. From a microstructural point of view, boron tended to destabilize the ferritic phase and to form iron and molybdenum borides. These borides can be found both in the intergranular regions, with a typical eutectic morphology, and dispersed in the ferritic matrix, in the form of nanometer-sized precipitates. This feature, having a significant effect on the hardness of the bulk material, has been ascribed to a bainite-like precipitation of borides from an undercooled austenitic phase.

Abstract: Thermodiffusion coatings (V+B) on steel have been obtained by an initial saturation with V followed by B. The properties of the diffusion layers, namely microstructure, microhardness, and phase composition, have been studied, and the influence of temperature and duration of treatment with V on steel on the thickness of the metallized layer and its phase composition has been determined. By increasing the temperature and duration of treatment with V on steel to more than 1200°C and 11 h, diffusion layers ∼350 μm thick and structures with clearly defined sublayers (zones) are obtained. VC is formed in the surface zone, which after boronizing turns into VB 2 .

Abstract: The effect of alloying additions of Ti and B on the process of micropyretic synthesis on NiAl and on the microstructure of the synthesized alloy was examined. It was observed that the combustibility of the quaternary alloy is good despite the presence of the alloying elements because of an additional combustion reaction between Ti and B. The microstructure of the quaternary alloy was found to consist primarily of the NiAl and Ti boride phases. The effect of preheating of the specimen prior to synthesis on the process of synthesis was also examined. It was observed that preheating not only can change the morphology of the phases but also influence the nature of the phases present in the alloy. The mechanism of the formation of the two phase microstructure during the synthesis from the elemental powders was established by stopping the combustion front and by carrying out a detailed microstructural characterization of regions around the stopped combustion front.

Abstract: The investigation of mechanical properties and failure mechanism of activated-diffusion-brazed (ADB) joints in IN-738 plate were conducted. Joints of this type, which had wide clearance, were formed using the brazing alloys Nicrobraz 150 and DF4B. The microstructural characterization showed that chromium borides with a blocky morphology were present in joints associated with the two brazing alloys. A major difference in matrix phase chemistry was observed, however, for the two brazing alloys, e.g., an Ni-B eutectic phase was observed in Nicrobraz 150, but DF4B exhibited a coarsened gamma prime (γ) phase and an absence of a nickel boride matrix phase. Results of tensile test showed that ADB specimens using DF4B brazing alloy exhibited 95% nominal tensile strength of IN-738 base materials. Fracture cracks in the joint area were initiated and confined to dispersed chromium boride sites. However, tensile test of ADB specimens using Nicrobraz 150 showed poor tensile properties at all testing temperatures, and their fractures were initiated at a brittle nickel boride site and propagated along the weak-bonded interface between the Ni-B eutectic phase and base materials.

Abstract: The stainless steel product has passive film on the surface, and at least one of a conductive metallic inclusion of carbide and a conductive metallic inclusion of boride protrudes through an outer surface of passive film from stainless steel under the passive film. The stainless steel product has low contact electrical resistance and suitable for use in bipolar plates of a polymer electrode fuel cell.

Abstract: A cermet powder for thermal spray coating, which is sprayed on a roll surface of a conveyer roll inside a furnace for heat treating a high tensile strength steel strip thereby to form a coating film, comprises: an alloy powder containing 3 to 8 mass % of Al, 16 to 25 mass % of Cr, 0.1 to 1 mass % of Y, and at least one of Co and Ni as the residual, with respect to the whole amount of the cermet powder; and a ceramic powder containing at least one of 1 to 5 mass % of a boride and 5 to 10 mass % of a carbide, with respect to the whole amount of the cermet powder.

Abstract: Fracture surfaces including those through indentations on different nanocrystalline boride/nitride films were investigated by FE-SEM, conventional SEM, and AFM. TiB2, TiN, Ti(B,N), AlN, and (Ti,Al)N films have been obtained by non-reactive r.f. magnetron sputtering. Deformation was realized by cleavage fracture and under a Vickers indentor. Two types of film fracture connected with homogeneous and inhomogeneous deformation are described and discussed. The analogy between the inhomogeneous deformation films image and the river pattern in the case of conventional ceramics is also pointed out.

Abstract: The interface reaction between a nickel-base, self-fluxing alloy coating and a steel substrate has been investigated to examine the formation of “pores,” which are observed along the interface of used boiler tubes. It was found that lumpy precipitates form along the interface instead of pores after heating at high temperatures and that the precipitates are of Fe2B boride. The adhesion strength of the coating is not decreased by the formation of Fe2B precipitates along the interface because of the increase of the adhesion due to interdiffusion.

Abstract: Ti2B5, TiB12, TiB≃25, TiB≃55, and TiB≃100 were prepared by self-propagating high-temperature synthesis and characterized by microstructural analysis, x-ray diffraction, and x-ray microanalysis. Data on the crystal structure, lattice parameters, and mechanical properties of the synthesized borides are presented.

Abstract: For applications at ultrahigh temperatures the multiphase microstructural options that can be developed in the Mo-Si-B system have demonstrated an effective and attractive balance of essential characteristics. The coexistence of the high melting point (>2100°C) ternary intermetallic Mo5SiB2 (T2) phase with Mo provides a useful option for in-situ toughening. A further enhancement is available from a precipitation reaction of Mo within the T2 phase that develops due to the temperature dependence of the solubility behavior of the T2 phase. However, direct access to Mo+T2 microstructures is not possible in ingot castings due to solidification segregation reactions that yield nonequilibrium boride and silicide phases with sluggish dissolution. Alternate routes involving rapid solidification of powders are effective in suppressing the segregation induced phases. The processing and microstructure options can also be augmented by selected refractory metal substitutional alloying, such as the incorporation of Nb, that alters the solubility of the T2 phase and the relative phase stability to yield solidification of two phase refractory solid solution + T2 structures directly. The observed alloying trends highlight the role of atomic size in influencing the relative stability of the T2 phase. A key component of the overall microstructural control and long term microstructural stability is determined by the kinetics of diffusional processes. The analysis of selected diffusion couples involving binary boride and silicide phases has been used to assess the relative diffusivities in the T2 phase and coexisting phases over the range of solubility and to provide a basis for the examination of the kinetics of reactions involved in coatings and oxidation.

Abstract: The hardness, elastic modulus, and elastic recovery of nanostructured boride/nitride films 1–2 µm thick have been investigated by the nanoindentation technique under the maximum loads over a wide range (from 5 to 100 mN). It is demonstrated that only the hardness parameters remain constant at small loads (5–30 mN). The data obtained are discussed and compared with the parameters determined by other methods.

Abstract: A method of adding boron to a tungsten, or tantalum, containing titanium aluminide alloy to form a boride dispersion in the tungsten, or tantalum, containing titanium aluminide. A molten tungsten, or tantalum, containing titanium aluminide alloy is formed and tungsten, or tantalum, boride is added to the molten tungsten, or tantalum, containing titanium aluminide alloy to form a molten mixture. The molten mixture is cooled and solidified to form a tungsten, or tantalum, containing titanium aluminide alloy having a uniform dispersion of tungsten, or tantalum, boride particles substantially without the formation of clusters of tungsten, or tantalum, boride. The titanium aluminide alloy comprises between 0.5 at % and 2.0 at % boron.

Abstract: The mechanical properties and fracture mechanism of irradiated and unirradiated boron containing Type 304 stainless steel are studied. Four different batches with different boron weight percentages are used. One of these batches was manufactured by a conventional wrought technique, while the others were manufactured by a powder metallurgy technique. The irradiated specimens were subjected to a fluence level of 5 x 10{sup 19} or 1 {times} 10{sup 21} n/m{sup 2}. The mechanical and fracture tests were performed at temperatures of 233, 298, and 533 K. No significant effects on the mechanical properties or fracture behavior were observed as a result of neutron irradiation and/or temperature. The ductility and toughness of the borated steel were found to decrease with increasing boron content. The effect of boride on void nucleation and linkage was found to play an important role in the fracture behavior of borated steel.